Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$155.70	13.610%	$176.8908	$176.89	$176.90	$176.90
Purchase #2	$45.31	6.795%	$48.3888	$48.39	$48.40	$48.40
Purchase #3	$147.34	3.555%	$152.5779	$152.58	$152.60	$152.60
Purchase #4	$82.79	7.820%	$89.2642	$89.26	$89.25	$89.30
Purchase #5	$55.31	10.538%	$61.1386	$61.14	$61.15	$61.10
Purchase #6	$206.51	13.659%	$234.7172	$234.72	$234.70	$234.70
Purchase #7	$104.39	7.542%	$112.2631	$112.26	$112.25	$112.30
7 purchase totals =	$797.35		$875.2406	$875.24	$875.25	$875.30